Lamp house for photographic enlarging and printing devices



March 22, 1966 THlELs 3,241,437

LAMP HOUSE FOR PHOTOGRAPHIC ENLARGING AND PRINTING DEVICES Filed June 10, 1963 2 Sheets-Sheet l Fla. 4

March 22, 1966 A. F. THIELS 3,241,437

LAMP HOUSE FOR PHOTOGRAPHIC ENLARGING AND PRINTING DEVICES Filed June 10, 1963 2 Sheets-Sheet 2 United States Patent 3,241,437 LAMP HOUSE FOR PHOTOGRAPHIC ENLARGING AND PRINTING DEVICES Albert Frans Thiels, Mortsel-Antwerp, Belgium, assignor to Gevaert Photo-Producten N.V., Mortsel, Belgium,

a Belgian company Filed June 10, 1963, Ser. No. 286,595 Claims priority, application Netherlands, June 28, 1962, 280,310/ 62 1 Claim. (Cl. 88--24) The present invention relates to a lamp house in enlarging and printing devices for the manufacture of photographic prints.

Lamp houses in photographic printing devices are known, comprising a projection lamp, a hollow mirror behind the projection lamp, a condenser and a heat absorbing filter in front of the projection lamp. In these lamp houses the required uniform light intensity is realized by positioning one or more light diffusing plates, having a relatively high density, between the light source and the negative holder. Furthermore the projection lamp is placed at a rather great distance from the plane of the negative holder in order to attain a uniform light distribution. For this purpose great dimensions of the lamp house are necessary. All these factors diminish the photometric efliciency of the lamp house.

The appearance of the so-called iodine lamps permitted the construction of a lamp house with a high photometric efliciency.

These iodine lamps comprise a tungsten filament in a cylindrical quartz tube. During the manufacturing iodine vapor is introduced into the tube. This lamp is 25% more efficient than the common incandescent lamps for an equal lamp life. At equal power this lamp has a much more compact form than the common incandescent lamps; moreover, the light intensity and its spectral characteristics remain practically constant in aging.

One object of the present invention is to provide a lamp house for photographic printers capable of producing a light output equivalent to or higher than that of condenser-type systems and in which the temperatures of the negative or transparency are maintained at safe levels.

Another object of the invention is to provide a lamp house which produces a light output with a very uniform light distribution and the spectral characteristics of which do not alter in aging.

Still another object of the invention is to provide a lamp house which is very simple in construction and which does not necessitate an expensive tooling equipment.

The lamp house according to the present invention comprises a reflector which is shaped in such a way that in the printing plane the sum of the directly radiated and the reflected light gives a uniform light intensity, a tube shaped iodine lamp inside this reflector, and a frame before the aperture of the reflector comprising at least one heat absorbing plate and one light ditfusing plate; as well as openings for the inlet and outlet of a cooling air current passing on either side over the heat absorbing plate.

As in practice the reflector aperture is mostlyrectangular, a reflector is needed, the ideal form of which is quite diflicult to realize.

According to a particular embodiment of the present invention the reflector is therefore constructed of flat reflecting metal strips which are folded to a discontinuous profile.

According to another particular embodiment of the present invention these metal strips are either pebbled, or etched in a semi-mat way, at the interior side of the reflector (by pebbled metal strips is meant that these strips have a ribbed or otherwise profiled uneven surface, in two directions perpendicular to each other).

3,241,437 Patented Mar. 22, 1966 The foregoing features and other special items of the present invention are described hereinafter by way of examples only.

FIG. 1 is a schematic representation of a printing device.

FIG. 2 is the light distribution obtained in the printing plane by means of a parabolic reflector.

FIG. 3 is the light distribution in the printing plane by means of a reflector in the lamp house according to the present invention (Without any diffusing plate).

FIG. 4 is a diagram of the sum of the directly radiated and the reflected light.

FIG. 5 is a longitudinal section of the lamp house according to the present invention on line 55 of FIG. 6.

FIG. 6 is a cross section of the lamp house on line 66 of FIG. 5.

FIG. 7 is a perspective view of another embodiment of the lamp house according to the present invention.

In FIG. 1 a printing device is illustrated schematically. It consists of the lamp house 11, the reflector 12, the iodine lamp 13, the frame 14 placed before the reflector aperture, the light diffusing plates 15 and 16 and a heat absorbing plate 17 in said frame, the negative 18 to be printed, the lens 19 and the printing plane 20 where the print material is positioned.

In the printing plane 20, a very uniform light intensity for the greatest size of the negative to be printed has to be obtained; this light intensity must be realized with a minimum of diffusing material because such material does not only disperse the light, but it also absorbs an amount of the light.

By using a reflector which presents a continuous profile at each arbitrarily chosen section, it is possible to obtain a perfectly uniform light intensity in the printing plane. In this case the interior side of the reflector can even be constructed with a mirror-like surface.

It has to be noticed that this theoretically ideal shape is different from the parabolic shape of a reflector which is quite well known in projectors and the like. The parabola shaped reflector has the property of radiating all the light rays of the light source as a parallel light beam. When a cross section of such a light beam is considered, it is seen that the light distribution is not uniform, and if such a parabolic reflector is used in the lamp house 11, then a light distribution in the printing plane 20 is obtained as represented by the plane 21 of FIG. 2. In this figure the light spot 22 represents an increased light intensity with respect to the other points of the plane 21, which phenomenon is a consequence of the direct radiation of the light source. A similar light distribution is obtained by using an elliptical reflector when the lamp and the lens are situated in the two focal points.

A representation of such a light distribution, no negative being positioned in the device, is practically realized by exposing in the printing plane 20 a sheet of photographic paper to the light of the lamp house (without any diffusing screen) and by afterwards developing said photographic paper in a contrasty way.

In practice, it is very diflicult to manufacture a reflector having a continuous profile allowing a perfectly uniform light distribution.

A particularly interesting embodiment showing a discontinuous profile is represented in detail in FIGURES 5 and 6.

In these figures 13 is the iodine lamp, 14 the frame in which the light diffusing plates 15 and 16 and the heat absorbing plate 17 are fitted, and in which also the manifold 23 for the cooling air, and the outlet openings 24 and 25 for said cooling air, are provided.

The reflector consists of the aluminum strips 26, 27 and 28. The rectangular aluminum strip 26, positioned on the longitudinal axis of the reflector, is folded on a broken V-line and has 5 reflecting planes; each of the wedge strips 27 and 28 positioned on the transverse axis of the reflector has four reflecting planes.

The aluminum strips 27 and 28 are attached to the strip 26 by inserting their narrow ending extremities into the slots of the horizontal part of strip 26. The reflector is fixed to the frame by means of the upper horizontal rims which are provided on the aluminum strips, and which are gripped between the frames 14 and 29. The frame 29 is provided with two tubes 39 and 31 of insulating material in the center of which respective contact elements 32 and 33 are fitted for contacting the electrodes of the iodine lamp 13. The reflector part 26 is provided with two openings 34 and 35 through which the iodine lamp is positioned into the reflector.

The interior wall 39 of the frame 14 has a mirror-like surface to limit the loss of light at the edges of the aperture. The result of the light distribution of the reflector is represented in FIG. 3. It can be seen that the central light spot is now surrounded by a great number of other light spots. This representation is practically realized in the manner already described for FIG. 2. The surrounding light spots result from the reflection of the light by the various reflecting planes of the reflector. The reflection in the longitudinal direction of the frame is realized by the two left hand and the two right hand planes of the part 26 of the reflector (FIG. 6). The reflection in the transverse direction occurs due to the four planes of each of the reflector parts 27 and 28 (FIG. 5).

The distribution of these light spots is not uniform (closer to each other the more the edges are approached to). It is determined in such a 'way that the sum 42, represented in dash and dot lines (FIG. 4), of the light directly radiated by the light source 13, represented by the curve 40, and of the light reflected by the reflector 12, represented by the curve 41, is constant over the printing plane. In the diagram of FIG. 4 the abscissa indicates the integration of the light intensity in the printing plane from one edge to the opposite edge. The ordinate indicates the'magnitude of the light-intensity. The number of reflecting planes is not limitative; instead of 35 luminous points (5 X7), a different number of luminous points can be chosen. However, the condition expressed by FIG. 4 should always be substantially complied with.

It is clear that by increasing the number of luminous points up to infinity, which means increasing the number of reflecting planes of the reflector up to infinity, viz. a continuously curved reflector surface, a perfectly uniformly lighted surface will be obtained. As for the pres ent example, however, owing to the well chosen unequal distribution of the light spots on the one hand, and the pebbled and/or semi-mat etched interior surface of the reflector, as well as the presence of the two light diffusing plates with low density in the frame before the reflector aperture on the other hand, a uniform light intensity in the plane of the positive print material is obtained. The loss of light caused by the light diffusing plates, and the semi-mat etched surface of the reflector, is but very small.

The exterior side of the reflector and of the protruding parts of the reflector part 26 are covered with a mat black paint, in order to assure a good heat radiation.

After being cut to size, the heat absorbing plate 17 is annealed to prevent bursting caused by the very high heating of the lamp 13.

The cooling air which is forced by a blower to circulate through the manifold 23 as indicated by the arrow, moves in the space defined by the light diffusing plates and 16, and carries off. the heat absorbed by the filter 17, leaving the said space through the openings 24, 25.

An iodine lamp of 625 w. 118 v. was used in the present examples. To increase the lamp life, the lamp was operated at under-voltage. An electric power of 350 watts was absorbed when the lamp was connected to an 80 volt supply.

In comparison with some existing lamp houses of automatic printing devices in which common 500 watt incandescent lamps are applied, it was found that the photometric efficiency of the lamp house according to the present invention was 13 times greater for white light. The rated 500 watts for this comparison was obtained by connecting the iodine lamp to a volt supply.

The efiiciency differs according to the spectral regions and amounts respectively to 11 in the red region, to 13 in the green region and to 15 in the blue region of the spectrum.

The efficiency in the blue region of the spectrum is higher (also owing to the spectral reflection properties of the aluminum reflector) and is therefore a further advantage, more especially in printing masked negatives which show a pronounced blue light absorption.

The light diffusing plate 16 is located only at a distance of a few millimeters from the plane of the negative 18, whereby the dispersion of the light passing through the negative increases so that scratches and like injuries on the negative material, are reproduced in the least sharp way possible on the positive print.

For printing small sized negatives a mask is placed before the surface 18, having an effective aperture of e.g. 24 x 36 mm. By using a mask with an aluminum covered side facing the light source instead of the usual mat black covering of said mask si-de, an increase of light of about 20% is obtained.

Since the light uniformity without the diffusing plate 15 suffices for miniature film, it is quite possible to replace this diffusing plate 15 by a clear one, whereby another increase of light of about 30% is obtained.

The described example relates to the printing of negatives on positive paper, the production of negatives and of duplicate positives from positives, etc.

Further, by providing the necessary color filters, one can make color prints on paper from color negatives, color diapositives from color negatives, color prints on paper from color diapositives, color intermediate negatives, etc. according to the additive or subtractive process.

It is evident that the lamp house according to the present invention is particularly suited for the additive printing method, wherein the partial exposures take place one after another, since this lamp house allows a considerable shortening of the relatively long printing times according to this method.

A second embodiment of the lamp house reflector, in which the iodine lamp is now positioned in the longitudinal direction of the reflector, is represented in FIG. 7.

Herein the reflector consists of a part 36, showing a continuously curved profile, and 2 flat sidewalls 37 and 38.

The filament length of the iodine lamp is equal to the length of the longitudinal side of the reflector aperture. Consequently, the light distribution is already constant in longitudinal direction so that only a uniform light distribution in the transverse direction must be assured. The latter light distribution is attained by the part 36 of the reflector having a continuously curved profile in the transverse direction. Due to this part 36 more light is reflected closer to the edges than in the center. Said part is etched in a semi-mat way whereas the interior surfaces of the flat side walls 37 and 38 are mirrorlike.

As a result thereof, a very good light distribution in the reflector aperture is obtained, so that even one single light diffusing plate with a very small density sufiices for obtaining a uniform illumination.

In the described example the filter 17 is a heat absorbing plate. It is quite clear that in a modified construction of the lamp house, this plate in the known way can also be a heat reflecting plate. It is also possible to use both types of plate in one and the same lamp house.

I claim:

A lamp house for use in printing or enlarging devices for manufacturing photographic prints, comprising a reflector which consists of a first rectangular aluminum strip which folded on a broken V-line and which is provided with two outer rims, the reflecting planes of said first strip running parallel to the longitudinal axis of the reflector, a second and a third wedge-shaped aluminum strip which are also folded on a broken line and each are provided with one outer rim, and which are inserted in the first folded strip, the reflecting planes of said second and said third strips running parallel to the transverse axis of the reflector, a tube-shaped iodine lamp, the axis of which runs parallel to the transverse axis of the reflector, which is positioned within the reflector with its electrode ends projecting through two opposite holes which are provided in the said first folded aluminum strip, a first rectangular frame before the reflector aperture and resting on the rims of the folded aluminum strips and a second rectangular frame resting on the opposite sides of said rims and which is fixed to said first frame so as to tightly grip the rims between the said frames, a heat absorbing plate and two light diffusing plates opposite and in parallelly spaced relation to said heat absorbing plate, which are mounted in said first frame, a manifold attached to one side of said first frame and a plurality of openings provided in the opposite side of the frame, for allowing the free passage of cooling air between the two light difrusing plates.

No references cited.

EVON C. BLUNK, Primary Examiner. NORTON ANSHER, Examiners. 

